A Design And Implementation Of Voltage Controlled And Temperature Compensated Oscillator(VCTCXO)

Crystal oscillator,as the frequency reference source of modern communication,precision instruments and other high-end fields,plays an important role in maintaining the normal and stable operation of instruments and equipment.Due to the physical characteristics of quartz crystal,the quartz resonator made of quartz crystal has very high quality factor and oscillation frequency,and quality factor is the necessary condition for the stability of the oscillator.Similarly,due to its physical characteristics,the frequency of quartz crystal oscillator gradually deviates from the center frequency with the change of temperature.If the crystal oscillator adopts the frequency modulation function based on the variable volume diode to design VCTCXO(Voltage Controlled and Temperature Compensated Oscillator),the frequency deviation caused by the change of temperature will increase with the increase of the frequency deviation,which is the so-called trim effect.In order to deal with the frequency instability caused by the Trim effect,combined with the principle of voltage control and temperature compensation,a variable capacity two stage tube is used to construct the Pearce oscillation circuit based on the inverter.The key point of this design is to obtain the accurate data of temperature frequency voltage and to fit it effectively,so two compensation schemes are adopted.The first one is based on the traditional least square method to fit the control curve,which is simple and effective.It can quickly calculate the control voltage through the microprocessor for feedback.However,due to the limitation of the compensation function itself,the control accuracy is insufficient.After the analysis of the error caused by the least square compensation,based on the traditional scheme,a new interpolation compensation scheme is proposed.This compensation function combines the least square method to fit the change trend of the function,and uses the original data to interpolate and modify the construction function.It can still quickly calculate the control voltage in real time,and at the same time,it can reduce the problem of control accuracy decline caused by the traditional scheme.This design starts from the principle of oscillation,studies the principle of starting oscillation,analyzes the LC oscillation circuit and quartz crystal resonator,and verifies it by simulation.It analyzes the high quality factor and frequency stability of quartz crystal oscillator,as well as the reason of frequency regulation by using varactor diode.In order to integrate into the digital circuit,pierce oscillation circuit is used,and then the hardware circuit,including the main control circuit for overall scheduling of storage control surface,the temperature measurement circuit for measuring real-time temperature,the DAC circuit for controlling the voltage of varactor,the power supply circuit for ensuring the voltage stability of PCB and the construction of download communication circuit are explained.Through the relevant chip documents,And according to the specific requirements,the driver and software are written and tested to meet the design requirements.Finally,the data acquisition and processing are carried out,and the fitting function is used to compare the two data acquisition schemes.The results show that the designed VCTCXO can reach the frequency stability of ± 1ppm in the temperature range of-30 ~ 70 ?,and the frequency adjustment range of ± 60 ppm,which achieves the expected goal of this design.